I installed notmuch from debian testing and it seems to work OK (from
the command line), e.g.

newmail@argo:~$ notmuch search blabla
thread:0000000000000001  Yest. 22:56 [1/1] fldsj@falma.de; blabla (inbox unread)

The maildir contains just one message.

Now I start up emacs, eval (require 'notmuch) and say M-x notmuch

Emacs now shows a buffer with the following contents

   Welcome to notmuch. You have 

And displays the following messages

Visit the notmuch website.
process-lines: notmuch exited with status 1

Clearly I am missing something trivial here, but I fail to find out
what.

Thanks,
Christoph